[GVN] Fix use-after-free in load PRE with select available value (#69314)

replaceValuesPerBlockEntry() only handled simple and coerced load
values, however the load may also be referenced by a select value.

Additionally, I suspect that the previous code might have been incorrect
if a load had an offset, as it always constructed the AvailableValue
from scratch.

Fixes https://github.com/llvm/llvm-project/issues/69301.

(cherry picked from commit 7f1733a2)